This invention relates to a telescopic boom for a crane with at least two telescopable telescoping sections in the form of lattice pieces, each of which exhibits a hollow structure that has in essence the shape of a box.
A goal in the sector of wind power plants is to achieve very large hub heights for the wind wheels, in order to obtain a wind power on the rotor blades that is as homogenous as possible. Therefore, during the assembly of wind power plants the maximum achievable hub height represents a characteristic value for the required hoisting devices, usually mobile cranes having telescopic booms.
Because of the requirement to provide very large boom systems with large boom lengths, there is the problem that such dimensions make conventional telescopic booms too heavy. A significant reduction in weight can be obtained with lattice booms. However, telescopable booms have the advantage over conventional lattice booms that they can be quickly converted from a transport state into a working state and take up significantly less space during assembly. An additional advantage is that the total center of gravity of a crane with a long erected boom is very high, a feature that renders moving the crane to the construction site in the erected state extremely problematic or even impossible.
In order to combine the advantages of the above described types, suggestions for telescopable lattice booms have already been put forth. However, one difficulty with such telescopic booms is that of securing the extended adjacent telescoping sections in relation to each other for crane operations. Usually, securing is achieved by means of a plurality of pinned joints between the inner and outer telescoping section.
German document DE 20 2010 014 105 U1 discloses a pinning system for connecting the individual lattice elements of a telescopable lattice boom. In order to connect, all four corner struts of the lattice elements to be connected are pinned to each other. However, the drawback with the disclosed solution is that a high machining accuracy is necessary during the manufacture of the boom, in particular the pinning system, so that the resulting production costs are rapidly driven upwards.